Production of benzene from a c5 to c7 hydrocarbon fraction



March 27, 1962 J. A. E. M ETAL 3,027,413

PRODUCTION BEN NE FROM A 0; TO 0 HY CAR FRACTION led July 1958 INVENTORS JOHN ARTHUR EDGAR M Y PETER THODQS WHITE AIAN' ARTHUR 1E0 irra NEYS United States Patent Ofitice 3,027,413 Patented Mar. 27, 1962 3,027,413 PRODUCTION OF BENZENE FROM A C TO C HYDROCARBON FRACTION John Arthur Edgar Moy, Peter Thomas White, and Alan Arthur Yeo, Sunbury-on-Thames, England, assignors to The British Petroleum Company Limited, Britannic House, London, England, a corporation of Great Britain Filed July 22, 1958, Ser. No. 750,087 4 Claims. (Cl. 260-672) This invention relates to the production of benzene from low boiling petroleum fractions by catalytic reforming.

With the progressive increase in the octane number of motor gasolines in recent years, there has been a corresponding decrease in the value of low boiling petroleum fractions as gasoline blending components, due to their relatively low octane number and to the difiiculty of upgrading them by hydroforming. Thus straight run fractions having an end boiling point of about 100-110 C. normally have an octane number of about 60 and are, moreover, not normally included in hydroforming feedstocks since they are not susceptible to upgrading by bydroforming. The economic utilisation of these low boiling relatively aromatic-free fractions (commonly known as light gasolines) is a current problem.

Hydroformates which are normally produced with research octane numbers of over 90 can at present be used in their entirety. However, total hydroformates cannot be used satisfactorily for gasolines with research octane numbers of 100 or more, and if there is a substantial increase in the demand for these gasolines, appreciable quantities of relatively low octane number hydroformate fractions may become available, for example the lower boiling relatively aromatic-free end of a hydroformate or a raffinate fraction of a solvent-extracted hydroformate.

These relatively aromatic-free and low octane number fractions, whether straight run or derived from treated material may be upgraded to increase their value as gasoline components by passing them over a dehydrocyclisation and dehydrogenation catalyst.

Another alternative use for these fractions is in the production of pure aromatics and the present invention provides a two-stage process for the production of benzene.

According to the present invention, a relatively aromatic-free hydrocarbon feedstock a major proportion of which boils below 100 C. is contacted at a temperature of at least 450 C. and at a pressure of not more than 50 p.s.i.g. with a dehydrocyclisation catalyst consisting essentially of chromia on alumina, the normally liquid product is then subjected to catalytic dealkylation to convert the alkyl aromatics present to benzene, and the dealkylated product is solvent-extracted and/or distilled to recover a substantially pure benzene fraction.

It is to be understood that the reference to a pressure of up to 50 p.s.i.g. includes operation at atmospheric pressure or below, operation at atmospheric pressure being in fact preferred.

The preferred space velocity is from 0.1 to 1.0 v./v./hr., particularly 0.1 to 0.5 v./v./hr. An appreciable quantity of hydrogen-rich gas is formed as a by-product and there is preferably no recycle of this gas, nor addition of extraneous hydrogen. To obtain the maximum quantity of benzene and alkyl aromatics in the dehydrocyclisation step the temperature should be above 525 C. The upper limit of temperature should be below that at which decomposition of the aromatics would occur, and may, conveniently, be in the region of 625 C. As the temperature is increased above 525 C., it has been found that the proportion of benzene and alkyl aromatics produced by weight of feed remains substantially constant irrespective of the severity of the process. Increased severity reduces the overall yield of liquid product by conversion of the remaining paraflins and any olefins which have been formed to gas, but the yield of benzene and alkyl aromatics itself is not substantially affected. High severity operation, therefore, gives a maximum yield of gas as by-product and by reducing the non-aromatic liquid yield may simplify the subsequent extraction and/ or fractionation.

At the upper limit of temperature, for example above about 580 C., there may be some decrease in the yield of benzene, due it is believed, not to the destruction of aromatics but to catalyst deactivation at the high temperatures used. A particularly preferred temperature range is from 525 to 580 C.

The feedstock may be any low-boiling hydrocarbon feedstock as hereinbefore defined, for example, a straight run petroleum fraction, a low-boiling fraction of a catalytic reformate, a raflinate fraction from a solvent extraction process, or a pure hydrocarbon. The proportion of aromatics in the feedstock has no significant effect on the process, but it is obviously economically undesirable to process a material already containing an appreciable quantity of the desired product. The term relatively aromatic free hydrocarbon feedstoc is to be understood in this light and a convenient figure may be not more than one third weight of aromatics by weight of feedstock. The feedstock preferably lies within the boiling range of about 35 to 120 C., particularly suitable feedstocks having an initial boiling point of from 35 to 50 C. and a final boiling point of from to C. The feedstock lying within the aforementioned boiling range is the feedstock consisting essentially of hydrocarbons having 5' to 7 carbon atoms in the molecule.

The chromia on alumina catalyst may advantageously contain promoters. For example, the catalyst may contain a minor proportion of an alkali metal, preferably potassium, and/or a minor proportion of a rare earth or mixture of rare earths. The preferred rare earth is cerium, and the promoters are preferably present in the form of their oxides. The relative proportions of the components by weight of total catalyst material stable at 550 C. maybe:

Chromium oxide 5% to 25%. Alkali metal (as oxide) 0.1% to 5%. Rare earth (as oxide) 0.1% to 5%. Alumina Balance.

Other promoters that may be used in the same proportions include boron, bismuth, germanium, nickel or manganese, preferably in the form of their oxides, with 3 or without an alkali metal, preferably potassium. Yet another effective promoter is a minor proportion of a 'spinel such as cobalt chromite, copper chromite, zinc 'titanate or iron chromite either as such or in the form of the naturally-occurring ore chrome ironstone.

The process according to the invention may be carried out with a fixed bed, a moving bed or a fluidised bed of catalyst. The process is particularly suitable for fluidised bed operation and the catalyst can be readily regenerated by conventional techniques.

Any convenient catalytic dealkylation step may be used to convert the alkyl aromatics, which with the low-boiling feedstocks used, will be largely toluene, to additional benzene. Nickel-alumina catalysts are preferred and a particularly suitable process uses a complex catalyst of nickel on a nickel alumina base. The nickel-alumina base may be prepared by impregnating alumina with a solution of a nickel compound decomposable under heat to nickel oxide, calcining the impregnated alumina at a temperature above 650 C. but below that at which appreciable transition to alpha-alumina occurs, and preferably, extracting the calcined alumina with an inorganic acid. This extraction step may conveniently use an aqueous acid of about 10% concentration at a temperature of about 100 C. for 15 to 30 minutes. This base is then impregated with a further solution of a nickel compound decomposable on heating to nickel oxide and is again calcined, preferably at a temperature in the range 350 to 650 C. The catalyst is preferably reduced before use. The preferred quantity of nickel in the catalyst base is l50% (more particularly 25-40%) by weight of the base and the preferred further quantity of nickel deposited on the base is 13O% (more particularly 10- 20%) by weight of total catalyst.

The dealkylation reaction is preferably carried out in the presence of added hydrogen or hydrogen-containing .gas (which may conveniently be obtained from the preyious dehydrocyclisation'step) at a temperature of from 250 .to 500 C. and a pressure of from atmospheric to 200 p.s.i.-g.

The subsequent solvent extraction and distillation stages may follow conventional practice and are preferably carried out under conditions to give a benzene fraction of greater than 99% purity. Unchanged alkyl aromatics are preferably recycled to the dealkylation stage and non-aromatic fractions may be recycled to the dehydrocyclisation stage. i

The invention is illustrated by the following example:

EXAMPLE were:

Pressure- Atmospheric. Space velocity 0.2 v./v./hr. Recycle gas None. Processing period 5 hours.

Three runs were carried out. The feedstocks, temperatures used and the results obtained are set out in Table 1 below:

Table 1 Lt. platinum Light gasreformatc 72.9 oline 61.2 Feed ON (Res) Clear ON (Res) (C C.) Clear (C O eratin Tern erature:

p (Ju .P 550 570 560 F 1, 022 1, 069 1, 040 Debutanised Product Hydrocarbon Type Analysis: w

Aromatics pcrocnt vol 75. 5 83. 5 45. 5 Olefins.. d 12 20 Saturates -d 12. 5 10. 5 34; 5 Aromatics percent Wt" 8 1 90 a3 Yields on feedstock:

Dehutanised product .percent wt 59 Aromatics"; do- 50 Benzene do on, 13-14 Toluene..- 0.--. ca 34- 5 m/p Xylen 0 ca 2 Aromatics in feed .do 16 Aromatics gain do 34 The table shows a gain in aromatics in each case of the order of 30%. It also shows the effect of increased temperature above 550 C. Withthe same feedstock (a light platinum reformate) the yield of aromatics differed by only 1% at 550 C. and 576 C. respectively although the overall yield was 5% less at the higher temperature.

The toluene contents of the debutanised products were converted to additional benzene by contacting the products in the presence of hydrogen, with a catalyst consisting of nickel on a nickel-alumina base. The dealkylation conditions were:

Temperature 797 F. (425 0). Pressure p.s.i.g.

Space velocity 0.45 v./v./hr. MolarH /hydrocarbon ratio 2:1.

A 60% wt. yield of benzene from toluene was obtained. The catalyst of nickel on a nickel-alumina base was prepared as follows:

An alumina gel was prepared by shaking 1600 grams of aluminum iso-propoxide with 3.5 liters of distilled water. Excess aqueous iso-propanol was removed by centrifuging. The moist gel was peptized with 48 ml. of glacial acetic acid and stirred to a smooth consistency whilst adding a solution consisting of 1200 grams of nickel nitrate hexahydrate in 200 ml. of water. This gel was dried at 140 C., crushed and sieved to a mesh size (6-12 British Standard Sieve) and roasted at a temperature of 900 C. for 2 hours.

The catalyst base so obtained was extracted with twice its volume of boiling 10% (volume) sulphuric acid. Three extractions were made, using fresh acid for each extraction, of durations of hour, /2 hour and 1% hours. Sufiicient stirring was applied to prevent bumping and the catalyst base was washed with water between each extraction until a colourless effluent was obtained. The extracted base was extracted by Soxhlet with distilled Water for 16 hours and dried at 140 C. The hot extracted catalyst base was added to a hot aqueous solution of g; nickel nitrate in 50 ml. water and allowed to impregnate for About in an oven at 110 C. The excess solution was filtered off and the catalyst roasted at 500 C. for 1 /2 hours. Before use the catalyst was heated at 500 C. for 16 hours in a stream of hydrogen.

Unconverted toluene after separation from the benzene and the non-aromatic compounds was recycled to the dealkylation step. Table 2 below sets out in flow sheet form, the treatment of the light gasoline according to the right hand column of Table 1 of the Example with figures showing the yield of the various products per 100.0 lb. of feed.

Table 2 Light Gasoline R 0.5% benzene i 540 lb. Loss I! negligible Carbon on catalyst -80 lb.

31% benezene 22% toluene olefins 27% saturates DEALKYLATION 530 lb. 46% benzene 3% toluene 51% non-aromatics Non-aromatics 280 EXTRACTION AND FRACTIONATION 5% aromatics E Benzene 235 lb.

99% pure Compositions given in percent weight. Weiglts of product streams to nearest 5 lb.

Table 3 Light Platinum Reformate Carbon on catalyst lb.

16% aromatics 2% olefins 82% saturates DEHYDROCYGLISA'IION 17% benzene 46% toluene 2.5% xylene 15.5% olefins 19% saturates DEALKYLATION 710 lb. 44% benzene 9% toluene 47% non-aromatics Stabiliser 30 Loss negligible Non-aromatics Toluene 6% aromatics EXTRACTION AND FRACTIONATION 99% pure Benzene The invention is further illustrated with reference to the accompanying drawing, in which a light hydrocarbon feedstock, for example, a light gasoline or the lower-boiling fraction of a catalytic refoi'rnate is passed through Gas 2350 s. 67% vol. Hz (:1580 s.c.f./b.) -320 lb.

Stabiliser overheads 60 lb.

Toluene concentrate (recycle) 15 lb. toluene line 1' to a dehydrocyclisation zone 2. The product is separated in zone 3 into a hydrogen-rich gas and a normally liquid product. The latter passes via line 4 to a dealkylatiou zone 5. A portion of the hydrogen-rich gas taken off overhead may also be fed to the dealkylation zone via line 6. The dealkylated product is again separated in Gas 1770 s.c.f./b. 77% vol. H2 (=l360 s.c.f./b.) 1b.

overheads 1b.

concentrate (recycle) 95% toluene 60 lb.

zone 7 into a hydrogen-rich gas, taken off overhead and recycled to the dealkylation zone 5 through line 8, and a normally-liquid product which is fed via line 9 to a solvent-extraction zone 10. Solvent entering by line 11 selectively extracts the aromatics which are principally benzene together with some unconverted toluene. A paraffinic raffinate is recovered through line 12 and the aromatic extract, after removal of the solvent, passes via line 13 to a fractionator 14. Substantially pure benzene is recovered overhead through line 15 and unconverted toluene is recycled through line 16 to the dealkylation zone 5.

We claim:

1. A process for the production of benzene comprising contacting a feedstock consisting essentially of a mixture of C to C non-aromatic hydrocarbons in a first reaction zone, with a dehydrocyclisation catalyst consisting essentially of 5 to 25% chromium oxide and balance alumina, at a temperature of from 525625 C. at a pressure not in excess of 50 psi. ga., at a space velocity of 0.1 to 1.0 v./v./hr., and in the absence of added hydrogen in the reaction zone, recovering the whole of the normally liquid product from the first reaction zone, contacting the whole of the normally liquid product in a second reaction zone with a dealkylation catalyst at a temperature of from 250 to 500 C., said temperature being lower than that employed in said first reaction zone, at a pressure not in excess of 200 psi. ga., and in the presence of added hydrogen in the second reaction zone, to convert alkyl aromatics of said liquid product into benzene, and recovering a substantially pure benzene fraction from the efiluent of the second reaction zone.

2. A process in accordance with claim 1, wherein the temperature in the first reaction zone is within the range 550-58 C.

3. A process in accordance with claim 1, wherein the dehydrocyclisation catalyst further contains 0.1 to of alkali metal, expressed as oxide, and 0.1 to 5% of a rare earth metal, expressed as oxide, both percentages being by weight of total catalyst material stable at 550 C.

4. A process for the production of benzene comprising contacting a feedstock consisting essentially of a mixture of C to C non-aromatic hydrocarbons in a first reaction zone, with a dehydrocyclisation catalyst consisting essentially of 5 to 25% chromium oxide and balance alumina, at a temperature of from 525-625 C., at a pressure not in excess of 50 psi. ga., at a space velocity of 0.1 to 1.0 v./v./hr., and in the absence of added hydrogen in the reaction zone, recovering the whole of the normally liquid product from the first reaction zone, contacting the recovered liquid product in a second reaction zone with a dealkylation catalyst consisting essentially of nickel on a nickel-alumina base, said nickel-alumina base containing 1 to 50% of nickel, by weight of the base, and l to of nickel, by weight of the total catalyst, deposited on the base, at a temperature of from 250 to 500 C., said temperature being lower than that of said first reaction zone, at a pressure not in excess of 200 p.s.i. ga., and in the presence of added hydrogen in the reaction zone, to convert alkyl aromatics of said liquid product into benzene, and recovering a substantially pure benzene fraction from the effiuent of the second reaction zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,436,923 Haensel Mar. 2, 1948 2,651,597 Corner et a1. Sept. 8, 1953 2,697,684 Hemminger et al Dec. 21, 1954 2,765,264 Pasik Oct. 2, 1956 2,780,661 Hemminger et al Feb. 5, 1957 

1. A PROCESS FOR THE PRODUCTION OF BENZENE COMPRISING CONTACTING A FEEDSTOCK CONSISTING ESSENTIALLY OF A MIXTURE OF C5 TO C7 NON-AROMATIC HYDROCARBONS IN A FIRST REACTION ZONE, WITH A DEHYDROCYCLISATION CATALYST CONSISTING ESSENTIALLY OF 5 TO 25% CHROMIUM OXIDE AND BALANCE ALUMINA, AT A TEMPERATURE OF FROM 525-625*C. AT A PRESSURE NOT IN EXCESS OF 50 P.S.I. GA., AT A SPACE VELOCITY OF 0.1 TO 1.0 V./V./HR., AND IN THE ABSENCE OF ADDED HYDROGEN IN THE REACTION ZONE, RECOVERING THE WHOLE OF THE NORMALLY LIQUID PRODUCT FROM THE FIRST REACTION ZONE, CONTACTING THE WHOLE OF THE NORMALLY LIQUID PRODUCT IN A SECOND REACTION ZONE WITH A DEALKYLATION CATALYST AT A TEMPERATURE OF FROM 250 TO 500*C., SAID TEMPERATURE BEING LOWER THAN THAT EMPLOYED IN SAID FIRST REACTION ZONE, AT A PRESSURE NOT IN EXCESS OF 200 P.S.I. GA., AND IN THE PRESENCE OF ADDED HYDROGEN IN THE SECOND REACTION ZONE, TO CONVERT ALKYL AROMATICS OF SAID LIQUID PRODUCT INTO BENZENE, AND RECOVERING A SUBSTANTIALLY PURE BENZENE FRACTION FROM THE EFFLUENT OF THE SECOND REACTION ZONE. 